Molded commutator



NOV. 3, 1953 Q -r 2,658,159

MOLDED COMMUTATOR Filed Dec. 22, 1949 IIIIm J 1/ z 5 7 J 4 at 351214;.

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Patented Nov. 3, 1953 MOLDED COBIMUTATOR Clarence A. Herbst, Park Ridge, 111., assignor to Resinoid Engineering Corporation, a corporation of Illinois Application December 22, 1949, Serial No. 134,569

3 Claims.

This application relates to a commutator for an electric machine and the method of manufacturing the same.

It is an object of this invention to provide a new and improved commutator for electric machines and a new method for easily and more economically manufacturing such commutator.

Another object is the provision of a new and improved method of preparing a tubular shell of electrical conductive material to receive an insulating core material to which the shell may be firmly bonded and then severed into separate commutator bars.

Another object is to provide a new and improved method of manufacturing a commutator in which a shell of electrical conductive material may be bonded to a core insulating material and then severed or cut into any number of desired commutator bars without adversely effecting the bond between each resultant bar and the core.

Another object is the provision of novel means for securing a bond between each commutator bar and a core of insulating material about which the bars are spaced.

Another object is to provide a commutator in which the bond between each bar and the insulati g core is distributed over substantially the whole core-contacting area of the bar.

Another object is to provide a method of manufacturing commutators in which a plurality of tangs are formed in the inner surface of a tubular shell of electrical conductive material, said shell is then bonded to an insulating core and then severed to form commutator bars each having generally the same number of tangs independent of the number of equal size bars cut from the shell.

Other objects and advantages will be apparent as the description of certain embodiments proceeds, taken in connection with the accompanying drawing, in which:

Fig. 1 is a side elevation of a tubular member of electrical conductive material showing in quarter section a spiral rib formed in the inner surface of the member;

Fig. 2 is an end View of the tubular member shown in Fig. 1 from which commutator bars may be formed;

Fig. 3 is a somewhat diagrammatical view of the swedging operation in which a swedging tool is in the process of forming tangs on the inner surface of the tubular member;

Fig. 4 is a side elevation partly in section of a tubular member having a spiral groove formed in its inner surface and swedged tangs formed over a portion of the inner surface;

Fig. 5 is a greatly enlarged view of a portion of the tubular member illustrated in Fig. 4 taken along a section longitudinal of the tubular member;

Fig. 6 is a partial cross section through a completed commutator, the left hand portion bein taken on a section line between tangs and the right hand portion being taken along a section line through the tangs; and

Fig. 7 is a greatly enlarged fragmentary plan view of a rib showing a crossgroove and tang formed therein.

While there is shown in the drawings and hereinafter described in detail a preferred form of the invention, it is to be understood that the invention is not limited to the particular form and arrangement shown. It is contemplated that various changes may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Commutators for electric machines have been constructed in a variety of sizes and ways, some of which have started with a plurality of separate bars arranged in a pattern to provide an outer exposed cylindrical surface, after which an insulating material has been forced in and around the separate bars to hold them in their proper insulated positions. Other methods have employed the use of a tubular member from which end portions are turned inwardly to grasp an insulating core, after which the tubular member is severed longitudinally to form separate commutator bars. In each of the above noted methods it has been necessary for the manufacturer to set up tools and machines to make a specific number of bars for the commutator as each bar of necessity had to be provided with means for anchoring it to the core. If the manufacturer desired to make the same diameter commutator having an additional bar, it was necessary that he completely change his machinery and cutting tools in order to make the change in his commutator. The equipment and machinery needed for such operations is expensive. I have perfected a method of manufacturing commutators for electric machines in which the above noted difficulties have been overcome and a more economical procedure has been evolved.

In Fig. 1 of the drawings a tubular member ID, which may have an outwardly extending flange II at one end is used as the starting material shape. The first operation performed upon the tubular member I0 is the cutting of a plurality of annular grooves l2 which may be formed as such or as one or more spiral grooves 12, in the inner surface of the member so that the grooves extend throughout the surface from one open end I3 of the member to the other open end I4. These grooves I2 ma be formed by a screw machine of a type which is well known and may be formed on successive tubular members ID by automatically controlling the machine. The grooves l2 are generally made with right angle corners and form ribs I5 projecting inwardly toward the center of the tubular member, which ribs have the same pitch as the groove I2 or are spaced apart equal distances in case the grooves I2 are annular. As seen in Fig. 1 the inner surface of the tubular member, after the grooving operation, has a very irregular longitudinal cross section.

After the ribs I5 and grooves I2 are formed in the inner surface of the tubular member, a swedging operation is carried out. As diagrammatically illustrated in Fig. 3 the member I is supported upon a pair of guide rollers I6 and a swedging tool I! having teeth I8 about its periphery is rolled over the exposed outer portions of the ribs I and swedges crossgrooves I9 in the upper surface of the rib. The swedging tool I! is of the gear tooth type and is rotated about its axis to impress the crossgrooves in the exposed surfaces of the ribs I5. In Fig. 5 it may be seen that the swedging operation forces portions of the ribs I5 outwardly from the ribs to form tangs 20 projecting from either side of each rib I5. The tangs 20 project into the grooves I2 so that the groove I2 at each crossgroove I9 has a dove-tailed configuration. After the ribs l5 and the crossgrooves l9 and the tangs 2B are formed in the inner surface of the tubular member, the

member is ready to receive a core of insulating material therein.

The method described above for forming ribs and crossgrooves and tangs requires only two machine operations upon the tubular member I0 which greatly decreases the cost of providing the necessary machinery in making the commutator.

Another method for forming dove-tailed grooves between the ribs is to roll with sufficient pressure the entire exposed end portions of the ribs I5 to flatten or expand the upper portion of the ribs thus making dove-tailed grooves between each of the adjacent ribs. If desired the grooves I2 may be undercut to form a dove-tailed rib extending in the manner of a helix from one end to the other of the tubular member. The crossgrooves I9 could then be impressed in the upper end portions of the ribs as described above thus preparing the member III to receive an insulating core.

A manufacturer desiring to work initially from flat stock may perform a first operation which consists of forcing a fiat piece of material about a mandrel to form a generally cylindrical member similar to the member I0 illustrated in Fig. 1. When using fiat material to start with it is not necessary to join the ends of the piece when forming the cylindrical member as the separation be.- tween the ends, may comprise a dividing space between commutator bars in the finished commutator. The manufacturer may also form ribs and grooves in a flat piece after which the crossgrooves may be swedged in the exposed end portions of the ribs while the piece is still fiat. If such material is used the flat piece may be forced around a mandrel parallel to the ribs to form a generally cylindrical member, again not joining the ends, and then the resultant tubular member will be properly prepared to receive a core of insulating material.

After the shell or cylindrical member has been prepared to receive an insulating material as above described a cylindrical liner 2| is held concentrically within the tubular member ID and the assembly is placed in a suitable press wherein insulating core 22 is molded in the tubular member. A preferred core material is a thermoreactive phenolic resin in combination with a heat resistant filler, usually asbestos fiber. Both the thermo-reactive phenolic resin and asbestos fillers are commercially available.

Referring now to Fig. 6 and particularly the left hand portion of the figure, it will be seen that the core material 22 flows into and fills the grooves I2 between the adjacent ribs I9 so that the material flows in and around each of the tangs 20. As will be seen from the right hand portion of Fig. 6 the core material 22 also fills the crossgrooves I9 formed in the exposed end portions of the ribs I5. The tangs 20 securely bond the shell III to the core material 22 and the crossgrooves l9 prevent the shell i0 from moving laterally of the core material 22. It will be noted that the ribs, crossgrooves and tangs are formed substantially throughout the inner surface of the tubular member I0 so that the bond between the member and the core is minutely distributed generally over the entire contacting surface between the core and member.

After the tubular member has been bonded securely to the core as above described the member may be severed as by sawing to divide the member into a plurality of commutator bars. With a given diameter of tubular member bonded to a core by the above described methods any number of bars desired may be formed of the tubular member without adversely affecting the bond between each resultant bar and the core since each bar will have generally an equal number of ribs, crossgrooves and tangs to securely bond the bar to the core. This method effects a great saving in manufacturing processes in that, with a given diameter of commutator any number of bars desired may be cut after the shell has been bonded to the core without the additional expense of setting up new machinery to secure more or less bars than the manufacturer had previously made for that diameter commutator.

In dividing the shell I0 into commutator bars the outwardly extending flange may be used to connect lead wires from the armature coils to the respective bars on the commutator in a manner that is well understood.

Examples of commutators which have been made and tested by the foregoing methods are given below as an aid to a complete understanding of this invention. However, they are not to .be construed as limiting the invention and are given for clearness of understanding only.

Example 1.--A copper tubular member having a wall thickness of and a brush diameter of 11%, the size generally used in automotive generators, was prepared by turning a spiral groove from one end to the other of the member, said groove having a depth of .030, a Width of .030" and a space between grooves of .030". Crossgrooves were then impressed (in the manner in dicated in Fig. 3) in the upper exposed portions of the ribs thus formed, said crossgrooves having a depth of .010, a width of 014-016" and a space between crossgrooves of .030". A core material as above described was then molded within the commutator shell and the shell was divided into 28 bars. The commutator was then placed 5 on testing machines and run for a considerable period of time at 20,000 R. P. M. No loosening of any bar was observed and the commutator thus formed was completely satisfactory. The standard test of the automotive industry for commutators of this size is 15,000 R. P. M.

Example 2.-A commutator having a diameter on the brushes was formed in a manner similar to the commutator set out in Example 1. The spiral groove formed in the inner surface of the commutator shell had a depth of .020", a width of .030" and space between adjacent grooves of .020". The swedge forming tool used had teeth spaced apart .023-024. This commutator was formed with a similar insulating core and divided into 5 bars and tested at 55,000 R. P. M. No loosening of the bars was observed and the commutator proved entirely satisfactory.

The examples given show that the bond between the core and shell is minutely distributed over the surface of the bar contacting the core. In Example 1 approximately 400 tangs per square inch of surface area were formed and in Example 2 approximately 800 tangs per square inch of surface area were formed. Thus if each shell is divided into six or twelve or any other number of bars, each bar will have many tangs bonding it to the core. The tangs are relatively small compared to the bar and are distributed over the entire inner surface of the bar, so that each tang I contributes to the bonding action between each bar and the core. I have defined this concept as being a minutely distributed bond.

From the foregoing description it will be readily apparent that there is herein disclosed a method of manufacturing commutators in which material comprising commutator bars in the finished product may be easily and economic-ally bonded to an insulating core and then cut into any desired number of bars. The bond between each bar and the core will be distributed over the surface of the bar contacting the core preventing any loosening of the bar. By the application of the herein disclosed methods, retooling of a manufacturers plant is not required to make the same size commutator with a different number of bars and a minimum of machinery is necessary for making different size commutators.

I claim:

1. A commutator comprising, drical core of insulating material, a plurality of electrical conductive commutator bars positioned about the periphery of said core, a plurality of undercut ribs extending from the inner surface of each bar transversely thereof with dovetailed grooves between each adjacent pair of ribs, said ribs having a plurality of crossgrooves transa generally cylinverse their exposed end portions, and said ribs extending into said core a distance suiiicient for said core material to fill said dovetailed grooves and crossgrooves to provide a distributed bond between each bar and the core.

2. A commutator comprising, a generally cylindrical core of insulating material, a plurality of electrical conductive commutator bars positioned in insulated relation one to the other about the periphery of said core, each of said bars having an arcuate outer exposed surface and an arcute inner surface facing the core, a plurality of parallel ribs and grooves in the inner surface of each bar extending transversely of said bar, said ribs and grooves being alternately positioned over the entire length of said inner surface, a plurality of individual tangs extending from each exposed edge of the inner end portion of each rib, and said ribs and tangs being embedded in said core to provide a distributed bond between each bar and the core.

3. A commutator comprising, a generally cylindrical core of insulating material, a plurality of electrical conductive commutator bars positioned in insulated relation one to the other about the periphery of said core, each of said bars having an arcuate outer exposed surface arranged along a circle of 1 1%- inches diameter and an arcuate inner surface facing the core, a plurality of parallel ribs and grooves in the inner surface of each bar extending transversely of said bar, said ribs having a depth and width of approximately 0.030 inch and said grooves being approximately 0.030 inch wide, a plurality of tangs extending from the exposed end portion of each rib, said tangs being spaced along a rib approximately 0.030 inch apart and having a width of approximately 0.015 inch, and said ribs and tangs being embedded in said core to provide a minutely distributed bond between each bar and the core.

CLARENCE A. HERBST.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,362,084 Dahl Dec. 14, 1920 1,426,293 Herrman Aug. 15, 1922 2,320,541 Wilson June 1, 1943 2,477,455 Hinchliff July 26, 1949 FOREIGN PATENTS Number Country Date 584,867 Great Britain Jan. 24, 1947 603,905 Great Britain June 24, 1948 768,521 France May 22, 1934 

